1. Field of the Invention
The present invention relates to a rotational transfer mechanism such as a one-way rotational transfer mechanism or a one-way clutch, and more specifically relates to the shape of a cam surface, provided in the rotational transfer mechanism, for transferring a torque of a rotary input shaft to a rotary output shaft.
2. Description of the Related Art
Among conventional one-way rotational transfer mechanisms having a rotary input shaft and a hollow-cylindrical rotary output shaft positioned radially outside the rotary input shaft, wherein the rotary input shaft is driven by motor to transfer rotation of the rotary input shaft to the hollow-cylindrical rotary output shaft, a one-way rotational transfer mechanism which prevents the motor from being rotated by rotation of the rotary output shaft (i.e., prevents the rotary input shaft from being rotated by rotation of the rotary output shaft) when the rotary output shaft is rotated has been disclosed in, e.g., Japanese Unexamined Patent Publication H08-177878 and Japanese Unexamined Patent Publication H11-202181.
In these conventional one-way rotational transfer mechanisms, one of opposed peripheral surfaces of the rotary input shaft and the rotary output shaft is formed as a torque transfer cylindrical surface having a circular cross section while the other peripheral surface of the rotary input shaft or the rotary output shaft is formed as a surface having a non-circular cross section to form a circumferentially-uneven-width space (accommodation space having different radial widths at different circumferential positions) between the opposed peripheral surfaces of the rotary input shaft and the rotary output shaft, so that torque transfer members (spherical members) are installed in the circumferentially-uneven-width space in a freely movable fashion. Rotating the rotary input shaft causes each torque transfer member to firstly move in the circumferentially-uneven-width space, subsequently wedge between an associated cam surface which forms a part of a circumferentially-uneven-width-space forming portion forming the aforementioned circumferentially-uneven-width space and the aforementioned torque transfer cylindrical surface, and finally transfer a torque of the rotary input shaft to the rotary output shaft.
In either of the above two patent publications, the shape of each cam surface, which forms a part of the aforementioned circumferentially-uneven-width-space forming portion, is determined so that the torque transfer member comes into contact with the associated cam surface at a predetermined point thereon when the torque transfer members come into contact with the torque transfer cylindrical surface of the rotary output shaft. However, the occurrence of dimensional errors in the cam surfaces and the torque transfer members in the production thereof cannot be avoided. Therefore, if such dimensional errors increase, each torque transfer member may come into contact with the associated cam surface at a point thereon which deviates from the predetermined point on the associated cam surface when the torque transfer members come into contact with the torque transfer cylindrical surface of the rotary output shaft; consequently, no torque can be transferred from the rotary input shaft to the rotary output shaft. Furthermore, each torque transfer member may wedge between the associated cam surface and the torque transfer cylindrical surface by an excessive force to a degree that makes it impossible for each torque transfer member to come out between the associated cam surface and the torque transfer cylindrical surface. These defects appear conspicuously especially when the one-way rotational transfer mechanism is miniaturized.